PROJECT SUMMARY: Zika virus (ZIKV) is a mosquito-transmitted flavivirus. It is associated with neurological features such as Guillain-Barre syndrome and microcephaly in the recent outbreak currently spreading through the Americas. Since there are no vaccines or specific antiviral treatments available for ZIKV, understanding its pathogenesis in humans is a high priority. Following mosquito infection, ZIKV is transported to the local draining lymph nodes, where primary amplification of the virus and key host defense responses are triggered. Although mosquito transmission is the primary means for infection, virus has been measured in seminal fluid, and sexual transmission has been reported on numerous occasions. In this proposal, we seek to study the early infection events that occur in humans in the draining lymph node as well as in the urogenital tract by developing ex vivo human lymphoid and cervical tissue models of ZIKV infection, respectively. In preliminary studies, we show that ZIKV replicates robustly in human lymphoid and cervical tissue in all donors tested, and ZIKV-infected cells can be detected. In this application, we will use two strains of ZIKV that may differ in their pathogenic potential in humans to: 1) determine the strain-specific replication kinetics following infection, 2) identify the ZIKV-positive cell population(s) within the tissues, and 3) evaluate the cellular immune response and cellular activation events in two distinct organ culture systems: lymphoid tissue (Aim 1) to mimic early infection in the draining lymph node, and cervicovaginal tissue (Aim 2) to mimic mucosal transmission. Understanding these viral and cellular aspects in a human system and how these differ between strains of ZIKV will not only provide the first glimpse into early infection events, but also lead to new hypotheses for in vivo susceptibility in humans.